Yet experts with these traits are often poor explainers, poor teachers - how then can their vital skills be transmitted?

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This is, I think, because systemizers do not see things in an overview, so they cannot provide a summary - but when they explain something they describe it as they experience it:

that is, they start at the beginning and go through to the end, without missing a step,

precision and completeness takes precedence over comprehension,

and this sequence may take a long time - too long for most people's attention span and absorptive ability.

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This is why so many tecchy people are so bad at explaining things.

And they cannot help themselves, because they are simply transmitting the world as they see the world.

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This is why formal teaching is limited and why apprenticeship is vital to the communication of skills.

Apprenticeship entails the master and the apprentice spending long periods of time working together for several years; and in these circumstances even the worst 'teacher' can pass on his skills to an eager student.

Apprenticeship is how traditional societies overcome the fact - the fact intrinsic to some types of expertise - that the people whose skills are most vital are often among the worst teachers.